System for controlling vehicle overspeeding via control of one or more exhaust brake devices

ABSTRACT

A method and system are provided for controlling overspeeding of a vehicle carrying an internal combustion engine having one or more exhaust brake devices controllable to apply braking torque to the engine. The system may be operable determine a desired speed of the vehicle, to determine a road speed of the vehicle, and if the road speed of the vehicle exceeds the desired speed of the vehicle by more than a threshold speed, to determine a target brake torque required to reduce the road speed of the vehicle speed to the desired speed of the vehicle, and to then control the one or more exhaust brake devices to apply the target brake torque to the engine to thereby control the road speed of the vehicle to the desired speed of the vehicle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Application No. 61/107,102, filed Oct. 21, 2008 which isexpressly incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to systems having one or moreexhaust brake devices, and more specifically to systems for controllingvehicle overspeed conditions by controlling one or more exhaust brakedevices.

BACKGROUND

Vehicle exhaust brake devices are generally known, and examples include,but are not limited to, variable geometry turbochargers, exhaustthrottle devices, and the like. It is desirable to control vehicleoverspeed conditions via control of one or more such exhaust brakedevices.

SUMMARY

The present invention may comprise one or more of the features recitedin the attached claims, and/or one or more of the following features andcombinations thereof. A method is provided for controlling overspeedingof a vehicle carrying an internal combustion engine having one or moreexhaust brake devices controllable to apply braking torque to theengine. The method may comprise determining a desired speed of thevehicle, determining a road speed of the vehicle, and if the road speedof the vehicle exceeds the desired speed of the vehicle by more than athreshold speed, determining a target brake torque required to reducethe road speed of the vehicle speed to the desired speed of the vehicle,and controlling the one or more exhaust brake devices to apply thetarget brake torque to the engine to thereby control the road speed ofthe vehicle to the desired speed of the vehicle.

In one embodiment, determining a desired speed of the vehicle maycomprise determining set speed of a cruise control system of thevehicle. Alternatively or additionally, determining a desired speed ofthe vehicle may comprise monitoring the road speed of the vehicle,monitoring operation of a service brake of the vehicle, determiningvehicle acceleration from the monitored road speed of the vehicle, anddetermining the desired speed of the vehicle over a time period based onvehicle acceleration over the time period and on a duration of the timeperiod in which the service brake of the vehicle was depressed.

In one embodiment, determining a target brake torque required to reducethe road speed of the vehicle to the desired speed of the vehicle maycomprise mapping the road speed of the vehicle and the desired speed ofthe vehicle to the target brake torque using a map that defines targetbrake torque values as functions of pairs of values of the road speedand the desired speed of the vehicle. Alternatively or additionally,determining a target brake torque required to reduce the road speed ofthe vehicle to the desired speed of the vehicle may comprise determininga speed error as a difference between the road speed of the vehicle andthe desired speed of the vehicle, and determining the target brake valuebased on the speed error. Determining the target brake value based onthe speed error may comprise controlling the speed error to the targetbrake value using a controller. Illustratively, determining the targetbrake value based on the speed error may comprise controlling the speederror to the target brake value using a proportional-integralcontroller.

Controlling the one or more exhaust brake devices may comprisedetermining a control setting of at least one of the one or more exhaustbrake devices based on the target brake torque, and controlling the atleast one of the one or more exhaust brake devices to the controlsetting. The method may further comprise determining a rotational speedof the engine, and determining a current barometric pressure.Determining a control setting of at least one of the one or more exhaustbrake devices may then comprise determining the control setting of theat least one of the one or more exhaust brake devices further based onthe rotational speed of the engine and on the current barometricpressure. In one embodiment, determining a control setting of at leastone of the one or more exhaust brake devices may comprise determining atarget vane position of a variable geometry turbocharger fluidly coupledto the engine based on the target brake torque, the rotational speed ofthe engine and the current barometric pressure. Controlling the at leastone of the one or more exhaust brake devices to the control setting maythen comprise controlling vanes of the variable geometry turbocharger tothe target vane position. Alternatively or additionally, determining acontrol setting of at least one of the one or more exhaust brake devicesmay comprise determining a target position of an exhaust throttle basedon the target brake torque, the rotational speed of the engine and thecurrent barometric pressure. Controlling the at least one of the one ormore exhaust brake devices to the control setting may then comprisecontrolling the exhaust throttle to the target position.

The method may further comprise determining a maximum available braketorque corresponding to a maximum available brake torque that may becurrently applied to the engine, and determining the target brake torqueas a minimum of the target brake torque and the maximum available braketorque value.

A system for controlling overspeeding of a vehicle carrying an internalcombustion engine may comprise a first speed sensor configured toproduce a speed signal indicative of road speed of the vehicle, anexhaust brake device responsive to a control signal to apply brakingtorque to the engine, a first control circuit including a memory havinginstructions stored therein that are executable by the first controlcircuit to determine a desired speed of the vehicle, and if the roadspeed of the vehicle exceeds the desired speed of the vehicle by morethan a threshold speed to determine a target brake torque required toreduce the road speed of the vehicle speed to the desired speed of thevehicle, and a second control circuit configured to control operation ofthe engine, the second control circuit including a memory havinginstructions stored therein that are executable by the second controlcircuit to produce the control signal based on the target brake torqueto thereby control the road speed of the vehicle to the desired speed ofthe vehicle.

The system may further comprise a datalink connected between the firstand second control circuits. The instructions stored in the memory ofthe second control circuit may further include instructions that areexecutable by the second control circuit to send to the first controlcircuit via the datalink a maximum available brake torque correspondingto a maximum available brake torque that may be currently applied to theengine. The instructions stored in the memory of the first controlcircuit may further include instructions that are executable by thefirst control circuit to determine the target brake torque as a minimumof the target brake torque and the maximum available brake torque value.

The instructions stored in the memory of the first control circuit mayinclude instructions that are executable by the first control circuit tosend the target brake torque to the second control circuit via thedatalink. The instructions stored in the memory of the second controlcircuit may further include instructions that are executable by thesecond control circuit to send to the first control circuit via thedatalink a maximum available brake torque corresponding to a maximumavailable brake torque that may be currently applied to the engine. Theinstructions stored in the memory of the first control circuit mayfurther include instructions that are executable by the first controlcircuit to determine the target brake torque as a minimum of the targetbrake torque and the maximum available brake torque value.

The system may further comprise an engine speed sensor configured toproduce an engine speed signal indicative of rotational speed of theengine, and a barometric pressure sensor configured to produce apressure signal indicative of current barometric pressure. Theinstructions stored in the memory of the second control circuit mayinclude instructions that are executable by the second control circuitto produce the control signal further based on the engine speed signaland on the pressure signal. In on embodiment, the exhaust brake devicemay comprises a variable geometry turbocharger having a number ofpositionable vanes, and the instructions stored in the memory of thesecond control circuit may include instructions that are executable bythe second control circuit to produce the control signal in the form ofa target vane position to thereby control the vanes of the variablegeometry turbocharger to the target vane position. Alternatively oradditionally, the exhaust brake device may comprise an exhaust throttleconfigured to restrict exhaust gas flow therethrough, and theinstructions stored in the memory of the second control circuit mayinclude instructions that are executable by the second control circuitto produce the control signal in the form of a target exhaust throttleposition to thereby control the exhaust throttle to the target vaneexhaust throttle position.

The instructions stored in the memory of the second control circuit mayfurther include instructions that are executable by the second controlcircuit to send to the first control circuit via the datalink a maximumavailable brake torque corresponding to a maximum available brake torquethat may be currently applied to the engine. The instructions stored inthe memory of the first control circuit may further include instructionsthat are executable by the first control circuit to determine the targetbrake torque as a minimum of the target brake torque and the maximumavailable brake torque value.

The system may further comprise a second speed sensor configured toproduce a speed signal indicative of rotational speed of an input shaftof a transmission, and means for determining a current barometricpressure. The instructions stored in the memory of the first controlcircuit may include instructions that are executable by the firstcontrol circuit to determine a control setting of the engine brakedevice based on the target brake torque, the speed signal produced bythe second sensor and the current barometric pressure, and to send thecontrol setting to the second control circuit. The instructions storedin the memory of the second control circuit may include instructionsthat are executable by the second control circuit to produce the controlsignal based on the control setting received from the first controlcircuit. In one embodiment, the exhaust brake device may comprise avariable geometry turbocharger having a number of positionable vanes. Inone embodiment, the instructions stored in the memory of the firstcontrol circuit may include instructions that are executable by thefirst control circuit to determine the control setting in the form of atarget vane position to thereby control the vanes of the variablegeometry turbocharger to the target vane position. Alternatively oradditionally, the exhaust brake device may comprise an exhaust throttleconfigured to restrict exhaust gas flow therethrough. The instructionsstored in the memory of the first control circuit may includeinstructions that are executable by the first control circuit to producethe control setting in the form of a target exhaust throttle position tothereby control the exhaust throttle to the target exhaust throttleposition.

The system may further comprise a datalink connected between the firstand second control circuits, and a cruise control system electricallyconnected to the second control circuit, the cruise control systemconfigured to produce a set speed for setting the road speed of thevehicle. The instructions stored in the memory of the second controlcircuit may further include instructions that are executable by thesecond control circuit to send to the first control circuit via thedatalink the desired vehicle speed in the form of the set speed of thecruise control system.

The vehicle may comprise a service brake and a service brake switchconfigured to produce a service brake signal corresponding to anoperational state of the service brake. The instructions stored in thememory of the first control circuit may include instructions that areexecutable by the first control circuit to determine vehicleacceleration from the speed signal produced by the first speed sensor,and to learn the desired speed of the vehicle over a time period basedon vehicle acceleration over the time period and on a duration of thetime period in which the service brake of the vehicle was depressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of one illustrative embodiment of a system forcontrolling vehicle overspeed conditions via control of one or moreexhaust brake devices.

FIG. 2 is a flowchart of one illustrative embodiment of a process forcontrolling vehicle overspeed conditions via control of one or moreexhaust brake devices.

FIG. 3 is a flowchart of one illustrative embodiment of a process forcarrying out the last step of the process illustrated in FIG. 2.

FIG. 4 is a logic diagram of one illustrative embodiment of a processfor determining control setting(s) for the one or more exhaust brakedevices.

FIG. 5 is a flowchart of another illustrative embodiment of a processfor carrying out the last step of the process illustrated in FIG. 2.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to a number of illustrativeembodiments shown in the attached drawings and specific language will beused to describe the same.

Referring now to FIG. 1, a block diagram and schematic view is shown ofone illustrative embodiment of a system 10 for controlling vehicleoverspeed conditions via control of one or more exhaust brake devices.In the illustrated embodiment, the system 10 includes an internalcombustion engine 12 that is configured to rotatably drive an outputshaft (not shown) that is coupled to an input shaft (not shown) of aconventional transmission 14. A rotatable output shaft 16 extends fromthe transmission 14 and is coupled via a conventional differentialassembly (not shown) to a rotatable axle that drives one or more wheelsof a vehicle carrying the engine 12 and transmission 14. Thetransmission 14 is conventional and illustratively includes a number ofautomatically selected gear ratios, although embodiments arecontemplated in which the transmission 14 includes one or more manuallyselectable gear ratios.

The engine 12 includes an air intake manifold 18 that is fluidly coupledto an air outlet of a compressor 20 of a conventional turbocharger 22via an air intake conduit 24. An air inlet of the compressor 20 isfluidly coupled via a conduit 26 to ambient. The turbocharger 22 furtherincludes a turbine 28 that is rotatably coupled to the compressor 20 viaa rotatably shaft 30, and an exhaust gas inlet of the turbine 28 isfluidly coupled to an exhaust manifold 32 of the engine 12 via anexhaust gas conduit 34. An exhaust gas outlet of the turbine 28 isfluidly coupled to ambient via an exhaust gas conduit 36. In theillustrated embodiment, the turbocharger 22 is a variable geometryturbocharger, meaning that the exhaust gas flow volume through theturbine 28 is selectively variable. In one embodiment, for example, theturbine 28 includes a number of conventional vanes that may beselectively positioned by a suitable actuator to thereby control theexhaust gas flow volume through the turbine 28. Alternatively, theturbine 28 may include other conventional geometry-varying structuresfor controlling the flow volume of exhaust gas through the turbine 28.In any case, the variable geometry turbocharger 22 is controllable todecrease, i.e., restrict, exhaust gas flow through the exhaust gasconduits 34 and 36, and/or to increase exhaust gas flow through theexhaust gas conduits 34 and 36. The control mechanism for accomplishingthis is illustrated in FIG. 1 by the diagonal arrow extending throughthe turbine 28.

In the illustrated embodiment, a conventional exhaust throttle 38 ispositioned between the exhaust gas outlet of the turbine 28 and ambient.The exhaust throttle 28 illustratively includes a valve or plate havinga position relative to the exhaust throttle 28 that is controllable viaa conventional actuator to restrict or increase exhaust gas flow throughthe throttle 28. Alternatively or additionally, the exhaust throttle 38may be substituted or augmented by a similar throttle interposed in theair intake conduit 24 between the compressor 20 of the turbocharger 22and the air intake manifold 18.

As they relate to the present disclosure, the variable geometryturbocharger 22 and the exhaust throttle 28 may be separately ortogether controlled to selectively restrict exhaust gas flowtherethrough. Restricting air flow through the engine 12 generally, andrestricting exhaust gas flow through the exhaust gas conduits 34 and 36specifically, imparts a retarding force on the engine 12 as is known inthe art. This retarding force results in a decrease in the rotationalspeed of the engine 12 which, applied through the drivetrain comprisingthe transmission 14, output shaft 16, differential and drive axle,causes the road speed of the vehicle to likewise decrease. The variablegeometry turbocharger 22 and the exhaust throttle 38 are referred toherein as exhaust brake devices.

The system 10 further includes an engine control circuit 40 thatincludes a memory unit 45. The engine control circuit 40 isillustratively microprocessor-based, and the memory unit 45 generallyincludes instructions stored therein that are executable by the enginecontrol circuit 40 to control operation of the engine 12, operation ofthe variable geometry turbocharger 22 and operation of the exhaustthrottle 38. It will be understood, however, that this disclosurecontemplates other embodiments in which the engine control circuit 40 isnot microprocessor-based, but is configured to control operation of theengine 12, the variable geometry turbocharger 22 and the exhaustthrottle 38 based on one or more sets of hardwired instructions and/orsoftware instructions stored in the memory unit 45.

In the system 10 illustrated in FIG. 1, a number of sensors, systems andactuators are electrically connected to the engine control circuit 40.For example, an engine speed sensor 42 is electrically connected to anengine speed input, ES, of the engine control circuit 40 via a signalpath 44. The engine speed sensor 42 is a conventional sensor, such as aHall-effect or other known sensor, and is configured to produce a speedsignal corresponding to rotational speed of the engine 12. The system 10further includes a conventional cruise control system 46 that iselectrically connected to a cruise control input port, CC, of the enginecontrol circuit 40 via a number, M, of signal paths 48, wherein M may beany positive integer. The cruise control system 46 is operable in aconventional manner to supply signals to the engine control circuit 40,based on manual input by the driver, corresponding to a desired roadspeed, e.g., “set” speed, of the vehicle. When a desired road speed hasbeen selected by the driver, the cruise control unit 46 suppliescorresponding signals to the engine control circuit 40, and the enginecontrol circuit 40 is responsive to these signals to control, pursuantto instructions stored in the memory unit 45, fueling and otheroperating parameters of the engine 12 in a conventional manner so thatthe road speed of the vehicle carrying the engine 12 is maintained atthe desired road speed value.

The system 10 further includes a conventional service brake switch orsensor 50 that is electrically connected to a brake sensor input, BS, ofthe engine control circuit 40 via a signal path 52. The service brakeswitch or sensor 50 produces a signal that corresponds to depression bythe driver of the service brake of the vehicle. The system 10 furtherincludes a barometric or ambient pressure sensor 54 that is electricallyconnected to a barometric pressure input, BP, of the engine controlcircuit 40 via a signal path 56. The barometric pressure sensor 54 maybe conventional, and is operable to produce a pressure signal thatcorresponds to ambient or barometric pressure.

The system 10 further includes one or more exhaust brake devices, asthis term has been defined herein. In the illustrated embodiment, forexample, a variable geometry turbocharger output, VGT, of the enginecontrol circuit 40 is electrically connected by a signal path 58 to anactuator (represented by the diagonal arrow through the turbine 28 inFIG. 1) that controls the flow volume of exhaust gas through the turbine28, e.g., by controlling the position of one or more turbine flowgeometry-determining turbine vanes. In the embodiment illustrated inFIG. 1, an exhaust throttle output, EXT, of the engine control circuit40 is electrically connected to the exhaust throttle 38 via a signalpath 60. The engine control circuit 40 is thus operable, pursuant toinstructions stored in the memory unit 45, to control operation of theturbine 28 and of the exhaust throttle 38. It should be understood,however, that other embodiments are contemplated in which the systemincludes only one of the exhaust brake devices.

The system 10 further includes a transmission control circuit 62 thatincludes a memory unit 65. The transmission control circuit 62 isillustratively microprocessor-based, and the memory unit 65 generallyincludes instructions stored therein that are executable by thetransmission control circuit 62 to control operation of the transmission14. It will be understood, however, that this disclosure contemplatesother embodiments in which the transmission control circuit 62 is notmicroprocessor-based, but is configured to control operation of thetransmission 14 based on one or more sets of hardwired instructionsand/or software instructions stored in the memory unit 65.

In the system 10 illustrated in FIG. 1, the transmission 14 includes anumber of sensors configured to produce sensor signals that areindicative of one or more operating states of the transmission 14. Forexample, an input shaft speed sensor 64 is positioned and configured toproduce a speed signal corresponding to the rotational speed of thetransmission input shaft (which is also the rotational speed of theoutput shaft of the engine 12). The speed sensor 64 may be conventionaland is electrically connected to a transmission input speed input, TIS,of the transmission control circuit 64 via a signal path 66, and thetransmission control circuit 62 is operable to process the speed signalproduced by the speed sensor 64 in a conventional manner to determinethe rotational speed of the transmission input shaft. The transmission14 further includes another speed sensor 68 that is positioned andconfigured to produce a speed signal corresponding to the rotationalspeed of the output shaft of the transmission 14. The speed sensor 68may be conventional and is electrically connected to a transmissionoutput speed input, TOS, of the transmission control circuit 62 via asignal path 70, and the transmission control circuit 62 is operable toprocess the speed signal produced by the speed sensor 68 in aconventional manner to determine the road speed of the vehicle carryingthe engine 12 and the transmission 14.

The engine control circuit 40 and the transmission control circuit 62each further includes a communication port, COM, and the twocommunication ports, COM, are electrically connected together via anumber, N, of signal paths 72, wherein N may be any positive integer.The one or more signal paths 72 are typically referred to as a datalink. Generally, the engine control circuit 40 and the transmissioncontrol circuit 62 are operable to share information via the data link72 in a conventional manner. In one embodiment, for example, the enginecontrol circuit 40 and transmission control circuit 462 are operable toshare information via the data link 72 in the form of messages inaccordance with a society of automotive engineers (SAE) J-1939communications protocol, although this disclosure contemplates otherembodiments in which the engine control circuit 40 and the transmissioncontrol circuit 62 are operable to share information via the data link72 in accordance with one or more other conventional communicationprotocols.

As it relates to this disclosure, the transmission control circuit 62 isoperable to receive certain operating information relating to operationof the engine 12 from the engine control circuit 40 via the data link 72in a conventional manner. For example, the engine control circuit 40 isconfigured in a conventional manner to continually send to thetransmission control circuit 62 via the data link 72 the “set” speed ofthe cruise control unit 46, i.e., the desired road speed produced by thecruise control unit 46, the status of the brake switch or current brakesensor signal produced by the brake switch or sensor 50 and the currentbarometric pressure signal produced by the barometric pressure sensor54. Alternatively or additionally, the brake switch or sensor signal andthe barometric pressure signal may be provided directly by the brakesensor/switch 50 and pressure sensor 54 respectively to the transmissioncontrol circuit 62 as shown by dashed-line representation in FIG. 1.

Referring now to FIG. 2, a flowchart is shown of one illustrativeembodiment of a process 100 for controlling vehicle overspeed conditionsvia control of one or more exhaust brake devices. In the illustratedembodiment, the process 100 is stored in the memory unit 65 of thetransmission control circuit 62 in the form of instructions that areexecutable by the transmission control circuit 62. Alternatively, partsof the process 100 may be stored in the memory unit 65 of thetransmission control circuit 62 in the form of instructions that areexecutable by the transmission control circuit 62 and other parts may bestored in the memory unit 45 of the engine control circuit 40 in theform of instructions that are executable by the engine control circuit40.

The process 100 begins at step 102 where the transmission controlcircuit 62 is operable to determine the desired vehicle speed, DVS. Incircumstances in which the cruise control unit 46 is active andproducing a desired or “set” speed signal, the engine control circuit 40is operable to continually send this desired speed value to thetransmission control circuit 62 via the data link 72, e.g., in the formof one or more broadcast messages. In circumstances in which the cruisecontrol unit 46 is not active or is otherwise not produced the desiredor “set” speed signal, the transmission control circuit 62 is operableto determine the desired road speed based on information from othersensors, switches and/or systems. In one embodiment, for example, thetransmission control circuit 62 is operable to continually monitor thecurrent road speed of the vehicle by monitoring the signal produced bythe transmission output shaft speed sensor 68, and to continuallymonitor the status of, or signal produced by, the service brake switchor sensor 50 and to process these signals to determine the desired roadspeed as a function of vehicle acceleration and service brake activationfrequency, duration and/or pressure. For example, the transmissioncontrol circuit 62 may be operable to continually monitor and learn thecurrent desired road speed over a recent time interval, and to determinethat the learned road speed is the desired road speed if the vehicleacceleration exceeds an acceleration threshold with the service brakeapplied. As another example, the transmission control circuit 62 may beoperable at step 102 to determine the desired vehicle speed bycontinually monitoring the vehicle road speed, and to calculate, e.g.,via one or more equations, tables, graphs, charts or the like, a desiredroad speed as a function of the current road speed, acceleration of thevehicle over a specified time period and a duration of this time periodthat the service brake was depressed. Those skilled in the art willrecognize other techniques for determining the desired road speed of thevehicle based on information provided by one or more sensors, switchedand/or systems when the cruise control unit 46 is not active or is nototherwise producing a desired road speed value, and any such othertechniques are contemplated by this disclosure.

From step 102, the process 100 advances to step 104 where thetransmission control circuit 62 is operable to determine the currentvehicle road speed, VRS. Illustratively, the transmission controlcircuit 62 is operable to determine the current vehicle road speed, VRS,by monitoring the speed signal produced by the transmission output shaftspeed sensor 68 and processing this signal in a conventional manner todetermine the current vehicle road speed. Alternatively or additionally,the system 10 may include one or more other speed sensors that aresuitably positioned relative to the vehicle and that produce a speedsignal that the transmission control circuit 62 may use to determine thecurrent vehicle road speed, VRS.

Following step 104, the process 100 advances to step 106 where thetransmission control circuit 62 is operable to determine whether thecurrent vehicle road speed, VRS, less the desired vehicle speed, DVS, isgreater than a speed threshold value, S_(TH). Generally, S_(TH) will beset to a value above which a vehicle overspeed condition is consideredto exist, e.g., 5 mph or other suitable value.

If, at step 106, the transmission control circuit 62 determines that thecurrent vehicle road speed, VRS, less the desired vehicle speed, DVS, isgreater than the speed threshold value, S_(TH), the process 100 advancesto step 108 where the transmission control circuit 62 is operable todetermine a brake torque value, BT, that would have to be applied to theengine 12 to reduce VRS to DVS. In one embodiment, the memory 65 has oneor more graphs, charts, tables, one or more equations or models or thelike stored therein that maps pairs of values of VRS and DVS tocorresponding brake torque values, BT. It will be understood that step108 may alternatively or additionally include more or fewer parametersfrom which to determine the brake torque values, BT, and any such moreor fewer parameters are contemplated by this disclosure. Examples of oneor more additional or alternative parameters that may be used todetermine the brake torque values, BT, may include, but are not limitedto, engine speed, e.g., using signals produced by the transmission inputshaft speed sensor 64, engine output torque, e.g., sent to thetransmission control circuit 62 by the engine control circuit 40 in theform of one or more messages broadcast on the data link 72, or the like.In an alternate embodiment, the transmission control circuit 62 includesa controller that determines determining a speed error as a differencebetween the road speed of the vehicle, VRS, and the desired speed of thevehicle, DVS, and that then determines the target brake value based onthe speed error in a conventional manner by controls the brake torquevalue, BT, to a value that minimizes the speed error. In one embodiment,such a controller may be implemented as a conventionalproportional-integral (PI) controller, although other conventionalcontroller configurations may alternatively be used.

The process 100 advances from step 108 to step 110 where thetransmission control circuit 62 is operable to determine a maximumavailable brake torque value, MBT. In one embodiment, the engine controlcircuit 40 is operable to continually compute the maximum availablebrake torque value in a conventional manner, e.g., based on a number ofengine operating conditions, and to continually send the computedmaximum available brake torque value to the transmission control circuit62 via the data link 72, e.g., in the form of one or more messagesbroadcast by the engine control circuit 40 onto the data link 72. Inthis embodiment, the transmission control circuit 62 is operable todetermine the maximum available brake torque value, MBT, at step 110 bymonitoring the communication port, COM, and receiving the maximumavailable brake torque values sent by the engine control circuit 40. Inalternative embodiments, the engine control circuit 40 may sendinformation to the transmission control circuit 62, e.g., via the datalink 72, from which the maximum available brake torque, MBT, may bedetermined. In this embodiment, the transmission control circuit 62 isoperable at step 110 to determine the maximum available brake torquevalue, MBT, by receiving information from the engine control circuit 40and computing MBT based on the received information.

Following step 110, the process 100 advances to step 112 where thetransmission control circuit 62 is operable to determine a target braketorque value, TBT, as a minimum of the brake torque value, BT,determined at step 108 and the maximum available brake torque value,MBT, determined at step 110.

If, at step 106, the transmission control circuit 62 determines that thevehicle road speed, VRS, less the desired vehicle speed, DVS, is notgreater than the speed threshold, S_(TH), the process 100 advances tostep 116 where the target brake torque value, TBT, is ramped to zero.The ramp rate of TBT at step 116 may be predetermined or may bedetermined as a function of one or more system operating parameters. Inany case, the process 100 advances from step 112 and from step 116 tostep 114 where the one or more exhaust brake devices described hereinare controlled based on the target brake torque value, TBT, to apply acorresponding target brake torque to the engine 12 and thereby controlthe road speed, VRS, of the vehicle to the desired vehicle speed, DVS.

Referring now to FIG. 3, a flowchart is shown of one illustrativeembodiment 114′ of step 114 of the process 100 illustrated in FIG. 1. Inthe illustrated embodiment, step 114′ includes a first step 120 in whichthe transmission control circuit 62 is operable to send the target braketorque, TBT, to the engine control circuit 40 via the data link 72. Theengine control circuit 72 is operable thereafter at step 122 to controlthe one or more exhaust brake devices, e.g., the variable geometryturbocharger 22 via the VGT output and/or the exhaust throttle 38 viathe EXT output, to apply a target brake torque corresponding to TBT tothe engine 12 and thereby control the road speed, VRS, of the vehicle tothe desired vehicle speed, DV.

Referring now to FIG. 4, a logic diagram is shown of one illustrativeembodiment of a control algorithm 150 that may be used by the enginecontrol circuit 140 at step 122 to control the one or more exhaust brakedevices to apply a brake torque corresponding to TBT to the engine 12.In the illustrated embodiment, the control algorithm includes a lowbarometric pressure map 152 having inputs receiving an engine speedvalue that was determined by the engine control circuit 40 from theengine speed signal, ES, and the target brake torque value, TBT,received from the transmission control circuit 62. The engine speedvalue and the target brake torque value, TBT, are likewise each appliedas inputs to a mid barometric pressure map 160 and a high barometricpressure map 168. Outputs of the maps 152, 160 and 166 are each providedas one input to a different multiplication block 156, 164 and 170respectively. The control algorithm 150 further includes three separatebarometric pressure multiplier blocks 154, 162 and 168, the outputs ofwhich are each provided as another input to the different multiplicationblocks 156, 164 and 170 respectively. Outputs of the threemultiplication blocks 156, 164 and 170 are all provided as inputs to asingle summation block 158, the output of which is a control signal, CS,that may be used to control either or both of the exhaust brake devices.

The low barometric pressure map 152 illustratively produces an exhaustbrake actuation signal, calibrated for low barometric pressure values,as a function of ES and TBT, and the barometric pressure multiplierblock produces a multiplier value, e.g., between 0 and 1, depending uponthe value of the barometric pressure signal, BP, relative to apredefined low barometric pressure value or range. For example, if thebarometric pressure is relatively low, the barometric pressuremultiplier value produced by the block 154 will be relatively high,whereas the barometric pressure multiplier value produced by the block154 will be relatively low if the barometric pressure value, BP, isrelatively high. The remaining blocks 160, 162 and 166, 168 functionsimilarly so that the actuator value produced by the summation block 158is a blend of actuator values for the current barometric pressure value,BT, relative to three different predetermined barometric pressure levelsor ranges. In embodiments in which VGT is used as the only exhaust brakecontrol mechanism, the control signal, CS, will typically be in the formof a turbine vane position or similar signal. In embodiments in whichEXT is used as the only exhaust brake control mechanism, the controlsignal, CS, will typically be in the form of a throttle positionrelative to a zero or maximum throttle position. In embodiments in whichVGT and EXT are both used as exhaust brake control mechanisms, thecontrol algorithm 150 may include two separate control structures of thetype just described, or may alternatively include a conventional controlstructure that blends operation of the variable geometry turbocharger 22and exhaust throttle 38 or that arbitrates control between the twodevices.

Referring now to FIG. 5, a flowchart is shown of another illustrativeembodiment 114″ of step 114 of the process 100 illustrated in FIG. 1. Inthe illustrated embodiment, the transmission control circuit 62 isoperable to determine the control signal, CS, and to provide the controlsignal, CS, to the engine control circuit 40 for direct control of theone or more exhaust brake devices. In this embodiment, step 114″includes a first step 180 in which the transmission control circuit 62is operable to determine the transmission input shaft speed, TIS, bymonitoring and processing the speed signal produced by the transmissioninput shaft speed sensor 64. Because the transmission input shaft isdriven directly by the engine, TIS generally represents the rotationalspeed, ES, of the engine 12. Thereafter at step 182, the transmissioncontrol circuit 162 is operable to determine the barometric pressure,BP. In the embodiment illustrated in FIG. 1, the transmission controlcircuit 62 is illustratively configured to carry out step 182 byreceiving the barometric pressure value, BP, from the engine controlcircuit 40 via the data link 72, e.g., in the form of messages broadcastby the engine control circuit 40 on the data link 72. In alternativeembodiments, such as shown by dashed line representation in FIG. 1, thetransmission control circuit 62 may have an input that is electricallyconnected to an output of the barometric pressure sensor 54, and in thisembodiment the transmission control circuit 62 is operable to carry outstep 182 by monitoring and processing the pressure signal produced bythe barometric pressure sensor 54.

Step 182 advances to step 184 where the transmission control circuit 62is operable to determine the exhaust brake device control signal orsettings, CS, as a function of the target brake torque value, TBT, thetransmission input shaft speed, TIS, and the barometric pressure value,BP. In one embodiment, the control algorithm 150 illustrated in FIG. 5is implemented in the memory unit 65 of the transmission control circuit62 and the transmission control circuit 62 is operable at step 184 todetermine the control signal or settings, CS, as described with respectto the control algorithm 150 of FIG. 5. Alternatively, the memory unit65 of the transmission control circuit 62 may include one or moreconventional algorithms for determining CS as a function of at leastTBT. In any case, step 184 advances to step 186 where the transmissioncontrol circuit 62 is operable to send the control signal or settings,CS, to the engine control circuit 40, e.g., via the data link 72 in theform of one or more messages broadcast by the transmission controlcircuit 62 on the data link 72. Thereafter at step 188, the enginecontrol circuit is operable to control the one or more engine brakedevices based on the control signal or settings, CS, received from thetransmission control circuit 62.

While the invention has been illustrated and described in detail in theforegoing drawings and description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly illustrative embodiments thereof have been shown and described andthat all changes and modifications that come within the spirit of theinvention are desired to be protected.

1. A method for controlling overspeeding of a vehicle carrying aninternal combustion engine having one or more exhaust brake devicescontrollable to apply braking torque to the engine, the methodcomprising: determining a desired speed of the vehicle, determining aroad speed of the vehicle, and if the road speed of the vehicle exceedsthe desired speed of the vehicle by more than a threshold speed,determining a target brake torque required to reduce the road speed ofthe vehicle speed to the desired speed of the vehicle, and controllingthe one or more exhaust brake devices to apply the target brake torqueto the engine to thereby control the road speed of the vehicle to thedesired speed of the vehicle.
 2. The method of claim 1 whereindetermining a desired speed of the vehicle comprises determining setspeed of a cruise control system of the vehicle.
 3. The method of claim1 wherein determining a desired speed of the vehicle comprises:monitoring the road speed of the vehicle, monitoring operation of aservice brake of the vehicle, determining vehicle acceleration from themonitored road speed of the vehicle, and determining the desired speedof the vehicle over a time period based on vehicle acceleration over thetime period and on a duration of the time period in which the servicebrake of the vehicle was depressed.
 4. The method of claim 1 whereindetermining a target brake torque required to reduce the road speed ofthe vehicle to the desired speed of the vehicle comprises mapping theroad speed of the vehicle and the desired speed of the vehicle to thetarget brake torque using a map that defines target brake torque valuesas functions of pairs of values of the road speed and the desired speedof the vehicle.
 5. The method of claim 1 wherein determining a targetbrake torque required to reduce the road speed of the vehicle to thedesired speed of the vehicle comprises: determining a speed error as adifference between the road speed of the vehicle and the desired speedof the vehicle, and determining the target brake value based on thespeed error.
 6. The method of claim 5 wherein determining the targetbrake value based on the speed error comprises controlling the speederror to the target brake value using a controller.
 7. The method ofclaim 6 wherein determining the target brake value based on the speederror comprises controlling the speed error to the target brake valueusing a proportional-integral controller.
 8. The method of claim 1wherein controlling the one or more exhaust brake devices comprises:determining a control setting of at least one of the one or more exhaustbrake devices based on the target brake torque, and controlling the atleast one of the one or more exhaust brake devices to the controlsetting.
 9. The method of claim 8 further comprising: determining arotational speed of the engine, and determining a current barometricpressure, wherein determining a control setting of at least one of theone or more exhaust brake devices comprises determining the controlsetting of the at least one of the one or more exhaust brake devicesfurther based on the rotational speed of the engine and on the currentbarometric pressure.
 10. The method of claim 9 wherein determining acontrol setting of at least one of the one or more exhaust brake devicescomprises determining a target vane position of a variable geometryturbocharger fluidly coupled to the engine based on the target braketorque, the rotational speed of the engine and the current barometricpressure, and wherein controlling the at least one of the one or moreexhaust brake devices to the control setting comprises controlling vanesof the variable geometry turbocharger to the target vane position. 11.The method of claim 9 wherein determining a control setting of at leastone of the one or more exhaust brake devices comprises determining atarget position of an exhaust throttle based on the target brake torque,the rotational speed of the engine and the current barometric pressure,and wherein controlling the at least one of the one or more exhaustbrake devices to the control setting comprises controlling the exhaustthrottle to the target position.
 12. The method of claim 1 furthercomprising: determining a maximum available brake torque correspondingto a maximum available brake torque that may be currently applied to theengine, and determining the target brake torque as a minimum of thetarget brake torque and the maximum available brake torque value.
 13. Asystem for controlling overspeeding of a vehicle carrying an internalcombustion engine, the system comprising: a first speed sensorconfigured to produce a speed signal indicative of road speed of thevehicle, an exhaust brake device responsive to a control signal to applybraking torque to the engine, a first control circuit including a memoryhaving instructions stored therein that are executable by the firstcontrol circuit to determine a desired speed of the vehicle, and if theroad speed of the vehicle exceeds the desired speed of the vehicle bymore than a threshold speed to determine a target brake torque requiredto reduce the road speed of the vehicle speed to the desired speed ofthe vehicle, and a second control circuit configured to controloperation of the engine, the second control circuit including a memoryhaving instructions stored therein that are executable by the secondcontrol circuit to produce the control signal based on the target braketorque to thereby control the road speed of the vehicle to the desiredspeed of the vehicle.
 14. The system of claim 13 further comprising adatalink connected between the first and second control circuits,wherein the instructions stored in the memory of the first controlcircuit include instructions that are executable by the first controlcircuit to send the target brake torque to the second control circuitvia the datalink.
 15. The system of claim 14 wherein the instructionsstored in the memory of the second control circuit further includeinstructions that are executable by the second control circuit to sendto the first control circuit via the datalink a maximum available braketorque corresponding to a maximum available brake torque that may becurrently applied to the engine, and wherein the instructions stored inthe memory of the first control circuit further include instructionsthat are executable by the first control circuit to determine the targetbrake torque as a minimum of the target brake torque and the maximumavailable brake torque value.
 16. The system of claim 14 furthercomprising: an engine speed sensor configured to produce an engine speedsignal indicative of rotational speed of the engine, and a barometricpressure sensor configured to produce a pressure signal indicative ofcurrent barometric pressure, and wherein the instructions stored in thememory of the second control circuit include instructions that areexecutable by the second control circuit to produce the control signalfurther based on the engine speed signal and on the pressure signal. 17.The system of claim 16 wherein the exhaust brake device comprises avariable geometry turbocharger having a number of positionable vanes,and wherein the instructions stored in the memory of the second controlcircuit include instructions that are executable by the second controlcircuit to produce the control signal in the form of a target vaneposition to thereby control the vanes of the variable geometryturbocharger to the target vane position.
 18. The system of claim 16wherein the exhaust brake device comprises an exhaust throttleconfigured to restrict exhaust gas flow therethrough, and wherein theinstructions stored in the memory of the second control circuit includeinstructions that are executable by the second control circuit toproduce the control signal in the form of a target exhaust throttleposition to thereby control the exhaust throttle to the target vaneexhaust throttle position.
 19. The system of claim 13 further comprisinga datalink connected between the first and second control circuits,wherein the instructions stored in the memory of the second controlcircuit further include instructions that are executable by the secondcontrol circuit to send to the first control circuit via the datalink amaximum available brake torque corresponding to a maximum availablebrake torque that may be currently applied to the engine, and whereinthe instructions stored in the memory of the first control circuitfurther include instructions that are executable by the first controlcircuit to determine the target brake torque as a minimum of the targetbrake torque and the maximum available brake torque value.
 20. Thesystem of claim 18 further comprising: a second speed sensor configuredto produce a speed signal indicative of rotational speed of an inputshaft of a transmission, and means for determining a current barometricpressure, wherein the instructions stored in the memory of the firstcontrol circuit include instructions that are executable by the firstcontrol circuit to determine a control setting of the engine brakedevice based on the target brake torque, the speed signal produced bythe second sensor and the current barometric pressure, and to send thecontrol setting to the second control circuit and wherein theinstructions stored in the memory of the second control circuit includeinstructions that are executable by the second control circuit toproduce the control signal based on the control setting received fromthe first control circuit.
 21. The system of claim 20 wherein theexhaust brake device comprises a variable geometry turbocharger having anumber of positionable vanes, and wherein the instructions stored in thememory of the first control circuit include instructions that areexecutable by the first control circuit to determine the control settingin the form of a target vane position to thereby control the vanes ofthe variable geometry turbocharger to the target vane position.
 22. Thesystem of claim 20 wherein the exhaust brake device comprises an exhaustthrottle configured to restrict exhaust gas flow therethrough, andwherein the instructions stored in the memory of the first controlcircuit include instructions that are executable by the first controlcircuit to produce the control setting in the form of a target exhaustthrottle position to thereby control the exhaust throttle to the targetvane exhaust throttle position.
 23. The system of claim 13 furthercomprising: a datalink connected between the first and second controlcircuits, and a cruise control system electrically connected to thesecond control circuit, the cruise control system configured to producea set speed for setting the road speed of the vehicle, wherein theinstructions stored in the memory of the second control circuit furtherinclude instructions that are executable by the second control circuitto send to the first control circuit via the datalink the desiredvehicle speed in the form of the set speed of the cruise control system.24. The system of claim 13 wherein the vehicle comprises a service brakeand a service brake switch configured to produce a service brake signalcorresponding to an operational state of the service brake, and whereinthe instructions stored in the memory of the first control circuitinclude instructions that are executable by the first control circuit todetermine vehicle acceleration from the speed signal produced by thefirst speed sensor, and to learn the desired speed of the vehicle over atime period based on vehicle acceleration over the time period and on aduration of the time period in which the service brake of the vehiclewas depressed.